Scanners for facsimile reproduction optically scan an original image to develop electrical signals representative of that image. These signals then can be processed, stored, combined with computer-generated data, transmitted to other locations and/or utilized in reproduction apparatus to reconstitute the image originally scanned.
The prior art has followed several approaches to facsimile reproduction, each approach depending upon various specific uses and objectives sought to be achieved. One prior art example is shown is U.S. Pat. No. 4,245,259 to Pick. There, an optical character recognition device constitutes part of a photocomposition system wherein a scanner is mounted for reciprocal movement over the image containing surface. This scanner reads the information on the surface during each traverse of the scanner. An apparently conventional roller drive controlled by a stepping motor advances the sheet longitudinally under the traversing shuttle mechanism. The reversal of this scanning shuttle, or scanning head, at each end of its movement is facilitated by springs mounted at the ends of the shuttle guide rod. Springs help to slow the scanner and to reverse its direction.
Another prior art device is described in Thaler U.S. Pat. No. 4,476,496. This is a facsimile device providing for periodic movement of the original sheet during the turnaround of the scanner at each end of its scanning traverse. Like the Pick apparatus, the Thaler machine incorporates spring stops at the end of the shuttle guides for assisting turnaround of the shuttle. Another similar scanner is described in U.S. Pat. No. 4,348,697 to Takahashi et al., which is capable of developing signals representing information for more than one scan line during each traverse of the carriage.
The technology represented by the foregoing patents has been used primarily in roster machines intended generally to minimize the cost of the machine. Unfortunately, these cost considerations ordinarily result in a sacrifice of reproduction accuracy or reproduction versatility (e.g., a limitation in the size of the area capable of being scanned with precision).
Scanner technology also has been used in the newspaper industry to prepare negatives to form printing plates from optically scanned sheets such as the "paste up" of a newspaper page. Of course, newspapers often require a higher degree of resolution with larger formats and faster throughputs than facsimile transmission machines for inter-office use. Machines capable of achieving higher resolution typically are either too slow or labor intensive for most newspapers. Moreover, many newspapers now utilize color formats on some of their pages. Such color formats require scanners which provide greater resolution and position of accuracy than those intended primarily for black and white reproduction.
One approach for achieving accuracy is to increase the size and mass of the components, thereby achieving better immunity from vibration and better stability. However, the moving parts in these high mass scanners inherently have been burdened with high mechanical accelerations and forces. The momentum attributable to these large rapidly moving components in prior art scanners can result in internally developed vibrations with a resultant decrease in accuracy.
The present invention preferably uses what is known as array scanning technology wherein, for each sweep of the scanning shuttle mechanism, several lines of information are developed. Such array technology is an outgrowth of photo-lithographic techniques developed by the semiconductor industry. Array technology has appeared in a number of recent scanners and printers. However, a review of this technology by experts in the field indicates that the performance of the first generation array printers and typesetters has not yielded the expected returns. The poor results have been attributed to the low cost, light-weight construction employed to reduce mechanical acceleration and forces inherent in more massive systems. This light-weight construction is prone to thermal and mechanical distortions which require frequent adjustment to correct for loss of precision.
In many prior single line, non array scanners operating at higher speeds, the sheet to be scanned moves continuously during the scanning operation. Alignment of the scanned data is thus skewed relative to the direction of movement of the sheet. The degree of skew is dependent upon the rate of movement of the original sheet and the speed or velocity of the scan line. This particular method of scanning has imposed limitations on both the speed and accuracy available. One such scanning system is shown in my earlier U.S. Pat. No. 4,131,916 in which the sheet to be scanned is carried on the inside of the stationary drum or curved surface. A scanning head mounted for movement at the axis of the curved surface is axially and rotationally movable on air bearing supports and is powered by suitable pneumatic drives. Such drum scanners are more prone to dimensional variations as a function of environmental changes, and have sacrificed productivity in order to achieve scanning efficiency and improved mechanical performance of the spinning laser.
Other known types of scanners, including those employing flat-bed imaging techniques, typically have relied upon mechanical or electrical motors to advance the media being scanned. The use of conventional electrical and electro-mechanical components to position the scanner and/or flat bed generally have not provided the desired degree of accuracy and speed for intermittent motion of a platen and high scanning rates.
A principal object of the present invention accordingly is to provide a scanner or recorder having the requisite geometric accuracy, resolution, large format and speed for present-day photocomposition, and at a cost which will make it affordable for small newspapers, engineering and other businesses.
Other objects of the invention are to reduce the mechanical forces and accelerations contributing to inaccuracies of known scanning systems, and to provide a scanner which achieves rapid and accurate intermittent motion of a flatbed platen carrying the media to be scanned or imaged.